The invention relates to a current stabilizing arrangement including a first and a second current path between a first and a second common terminal, a first current-dividing circuit having transistors of a first conductivity type and having an input circuit with a low input impedance and an output circuit with a high output impedance, and a second current-dividing circuit comprising transistors of a second conductivity type and also having an input circuit with a low input impedance and an output circuit with a high output impedance, the first current-dividing circuit defining the ratio between the currents flowing in the two current paths and the second current-dividing circuit defining the absolute values of the currents flowing in the two current paths by means of a semiconductor junction connected in parallel with the series arrangement of a semiconductor junction and a first resistor, which current stabilizer also includes means for starting the current-stabilizing arrangement.
Herein, a current-stabilizing arrangement in general is to be understood to mean a circuit arrangement in which the ratio between the currents in the input and the output current path is defined unambiguously by a parallel arrangement of semiconductor junctions, whether or not in combination with resistors.
Such a current-stabilizing arrangement is disclosed in, for example, German patent application No. 2,140,692, which has been laid open to public inspection. A problem associated with such current-stabilizing arrangements is that, apart from a stable state in which the desired currents flow, they also have a stable state in which the currents are zero. This means that these current-stabilizing arrangements require an additional starting circuit which ensures that when the power supply is switched on the arrangement occupies the desired stable state in which the currents are not zero.
In the current-stabilizing arrangement in German patent application No. 2,140,692, this starting circuit includes the series arrangement of a resistor and two diodes, poled in the forward direction between the two power-supply terminals, and a third diode which connects the junction point of the resistor and one of the diodes to a suitable connection point of the current-stabilizing arrangement. When the power supply is switched on, a current will flow in the series arrangement of the resistor and the diodes, so that such a voltage appears across the series arrangement of the two diodes that the third diode is biassed in the forward direction and, via this third diode, a starting current is supplied to the connection point, owing to which a current will flow in the current-stabilizing arrangement and the arrangement assumes the desired stable state. The connection point has been selected so that when the current-stabilizing arrangement has assumed the desired stable state the third diode is biassed in the reverse direction and is consequently cut off.
The use of such a starting circuit has the disadvantage that during starting the voltage across the two diodes poled in the forward direction also appears across the series arrangement of one diode and two base-emitter junctions which is arranged in parallel with said two diodes, i.e. across three base-emitter junctions in total, so that the starting current, which is the current through these base-emitter junctions, will be very small. Therefore, starting of the arrangement is not always guaranteed. Moreover, the total current consumed by the stabilizing arrangement is not stabilized because the starting circuit consumes a certain non-stabilized current.
In the current-stabilizing arrangement described in German patent application No. 2,157,756, the starting circuit comprises a leakage current source which supplies a leakage current to one of the two current paths of the arrangement in order to obtain the desired state with non-zero currents during switching on. Such a starting circuit has the disadvantage that after the arrangement has been started the leakage current keeps flowing in one of the two current paths and thereby affects the operation of the current stabilizer. In order to minimize this effect the leakage current must be substantially smaller than the stabilized currents in the two current paths. However, if the stabilizer current is small, the leakage current becomes impracticably small. The use of a leakage-current source also has the disadvantage that, due to the temperature dependence of the leakage current at low temperatures, the leakage current becomes so small that it is no longer capable of starting the arrangement.